Effect of electronic nature of emission layer materials on emission region in organic thin-film electroluminescent devices

Summary form only given. We have fabricated organic thin-film electroluminescent (EL) devices using 9,10-bisstyrylanthracene derivatives (BSA´s) with different substituents, electron withdrawing or electron donating groups, as emission layer materials and shown that the performance of EL devices are largely dependent on the electronic nature of emission layer materials. In this report, we clarify the effect of electronic nature of emission layer materials on emission region in order to understand the relationship between the performance of EL devices and the electronic nature of emission layer materials farther. We used two 9,10-bisstyrylanthracene derivatives, which had cyano groups as an electron withdrawing group (BSA-1) or diphenylamino groups as an electron donating group (BSA-2), for emission layer materials. We fabricated some devices partially doped with a Squarilium dye within emission layers and investigated the dependence of EL spectra on doped position in emission layers. In the single-layer device with BSA-1 as an emission layer, emission was mainly located at the side of anode. In the contrary, emission occurred through the emission layer except the region near cathode in the single-layer device with BSA-2 as an emission layer. These results correspond to our previous discussion; BSA-1 has electron injection/transport capability and BSA-2 has the specific electronic nature which allowed the transport of both electrons and holes.